The compounds of the above-mentioned formula (I) are highly selective and long-acting antagonists of α2-adrenoceptors. The compounds are especially valuable in the treatment of cognitive disorders. Compounds of formula (I) and their preparation have been described in patent publication EP 0 618 906 B1. Specific examples of such compounds are 4-(2-ethyl-5-fluoroindan-2-yl)-1H-imidazole, i.e. fipamezole, and 4-(5-fluoroindan-2-yl)-1H-imidazole.
Although the compounds of formula (I) and their salts have good properties as such, they have disadvantages, when formulated for conventional oral administration, i.e. the normal route for administering said compounds. A problem is that the compounds rather quickly decompose in the gastrointestinal area or other body systems prior to accessing systemic blood flow and the therapeutic target organs. This in turn significantly lowers the effect of the compounds in question.
Toxicology studies carried out with dogs (see Example 8) have further suggested that cardiac safety considerations are of importance whereas QT prolongation was observed with high oral doses of fipamezole when the systemic concentration of fipamezole reached about 2000 ng/ml.